1. Field of Invention
The invention relates generally to detecting and characterizing fractures in a subterranean wellbore. More specifically, the present invention relates to a device and method that uses a radiation source for inspecting a subterranean formation and a radiation detector for detecting or identifying the presence of fractures in a formation adjacent the tubular.
2. Description of Prior Art
Subterranean wellbores used for producing hydrocarbons typically are lined with a casing string that is cemented to the formation intersected by the wellbore. The casing and the surrounding formation are then perforated to provide fluid communication between the formation and interior of the casing. Fluid produced from the well flows through the perforations, to within the casing, and to the surface within production tubing that is inserted inside the inner casing string.
Some hydrocarbon bearing formations can have low permeability due to the presence of shale, or very tight formation rock (such as in limestone formations); which in turn can limit hydrocarbon production. However, natural or man-made fractures in these formations can increase formation permeability thereby increasing hydrocarbon production. Identifying the location and size of these fractures are of considerable importance in determining which part of the borehole to perforate and produce. Often, a layer of shale is on top of a formation that contains hydrocarbons. Generally, it is more stable to drill in the layer of shale than the hydrocarbon bearing formation. In these situations, a wellbore is drilled through the shale with the hopes of intersecting a fracture in the shale that extends into the reservoir having the hydrocarbons, as fractures increase permeability of a subterranean formation.